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Is the War on Salt Justified?

Aug 5, 2011 at 10:16 AM Chime in now

War on salt


By JULIA BELLUZ, Macleans.ca

The Statement: “People who eat a high-sodium diet can be putting themselves at risk of high blood pressure that can lead to heart attack and stroke.”—The Chronicle Herald, 08/03/2011

After decades of attempts by policy makers to wean people off the white stuff, it is now taboo to grab the salt shaker at a restaurant and pour it like snow on your dinner. The wisdom that salt is bad is often reinforced in the media. Just this week, the Chronicle Herald ran a piece about how to “shake your salt habit,” as if sodium were akin to tobacco or cocaine. The Globe and Mail also published on a new scare study, which revealed that 70 per cent of infants consume too much salt. Parents were warned that side-effects could be “more serious than having bloated babies… too much salt in an infant can lead to poor kidney development (and kidneys are the organs that help us skim salt from our blood).”

But what kind of evidence do we have to justify the war on salt?

Let’s start with the most recent Cochrane systematic review, published last month, on the effects of restricting salt consumption. The authors found that—even after collecting more data than previous systematic reviews on this subject—there was no clear evidence to show that cutting back on salt reduces the risk for heart attacks, strokes or death in people with both normal and high blood pressure.

Another recent (though controversial—see this link) study, published in the May 4 issue of The Journal of the American Medical Association, found that the less salt people consumed, the more likely they were to die of heart disease. Dr. Jan A. Staessen, the study’s lead author, told the New York Times, “If the goal is to prevent hypertension (with lower sodium consumption) this study shows it does not work.”

The tenuousness of the link between reduced salt consumption and good health has been demonstrated in earlier studies, which have concluded that there is not enough evidence to assess the effects of reduced salt intake on mortality or cardiovascular events like strokes and heart attacks. For example, a 2002 systematic review published in the British Medical Journal stated that a policy of reduction in salt intake for an entire population “can achieve small reduction in blood pressure across the whole population for sustained period of time [...] However, raised blood pressure is only one risk factor for cardiovascular disease and overall clinical benefits (or harms) of a low sodium diet are unclear.”

In 2008, a systematic review entitled, “Effects of low sodium diet versus high sodium diet on blood pressure, renin, aldosterone, catecholamines, cholesterols, and triglyceride” delved into the salt controversy, and came out with similarly muddled conclusions. “Short-term studies show that in people with elevated blood pressure low salt diets lead to drops in blood pressure, but overall harms or benefits are not known.” The researchers behind the study, including Dr. Niels Graudal of the Copenhagen University Hospital, suggested that those with normal blood pressure should not reduce the amount of salt they consume.

Science-ish contacted Dr. Graudal to get some advice about what would happen if a person decided to reduce his or her daily sodium intake by about 50 per cent, from a normal level of some 3.5g (the Canadian average) to about 1.8g. He said that while this dietary change will mean reduced blood pressure in healthy people and those with high blood pressure, it will also activate the sodium conserving endocrine system, resulting in an increase in renin (an enzyme in the kidneys that promotes the production of angiotensin, which are peptides that control blood pressure) and aldosterone (a hormone that regulates salt and water balance in the body). As well, the dietary change will activate the sympathetic nervous system and may increase the levels of triglyceride and cholesterol in the blood. “The effect on blood pressure, although small, may be good, the other effects may be bad,” he said. “Nobody knows what the net effect of all these effects are on morbidity and mortality.”

He also warned that people should be wary of a lesser-known salt hazard: consuming too little. “Very low levels of sodium may lead to hyponatriaemia (low sodium concentration in the blood), which is dangerous and may lead to brain damage and in the worst case death.” He added: “Sodium is one of the most essential components of the body without which life is not possible.”

More from Macleans.ca:
Antioxidants: Can they save you or kill you quicker?

How do you know when to get screened for breast cancer?

Will those genetically modified soy beans make you sick?




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